**7. Mineral fertilization**

The mineral fertilization of sugarcane is based on the results of soil analysis at the 0–20 cm layer and on the productivity desired.

[19, 20]. However, in an experiment conducted by [3] with plant cane cultivated in a sandy soil and fertilized with marked urea (15N), losses were not observed with the leaching of nitrogen from the fertilizer (**Figure 5**). The movement of the 15N-fertilizer was small. More than 70% of the fertilizer recovered in the soil was at the 0–30 cm layer. There was a measurable loss of N native from the soil, or of crop remains, equivalent to 4.5 kg ha−1 [3]. Thus, if nitrogen fertilization is applied to plant cane, nitrogen fertilizer, at doses ranging from 60 to 100 kg ha−1, should

Mineral Nutrition and Fertilization of Sugarcane http://dx.doi.org/10.5772/intechopen.72300 179

The responses of sugarcane regrowth to nitrogen fertilization are more frequent than in plant cane, with a percentage above 90%. As a general recommendation, it is suggested to apply 1.0 kg of N per ton of natural matter accumulated in shoots. Since industrializable culms represent on average 80% of the natural matter of shoots, yields of 100 t of culms would correspond to 125 t of natural matter. In this case, the recommendation for fertilization would be 125 kg of N ha−1, and the nitrogen fertilizer should be applied in a single dose together with potassium.

Urea has been the most used nitrogen fertilizer for sugarcane fertilization mainly because of its lower cost per unit of N compared to other sources. The application of urea to the soil or straw may lead to large losses due to the volatilization of ammonia (approximately 40%) [1]. Therefore, it is recommended to bury it into the soil at a depth of approximately 7.0 cm. When it is not possible to bury the urea in the soil, it must be irrigated to incorporate it into the soil or to fertilize it before a rain, which is possible only in small areas. If it is not possible to bury

**Figure 5.** Nitrate uptake by corn plants with different phosphorus supplies: adequate before and during the study (+P; +P), adequate before and absent during the study (+P; −P), absent before and adequate during the study (−P; +P), and

absent before and during the study (−P; −P). Source: adapted from [18].

be applied to the bottom of planting grooves along with phosphorus and potassium.

**7.2. Nitrogen in regrowth**

### **7.1. Nitrogen in plant cane**

Nitrogen is important for the nutrition and physiology of sugarcane because, among other functions, it is a constituent of all amino acids, proteins, enzymes, and nucleic acids [17]. Nitrogen and potassium are absorbed in greater amounts by this crop [3]. The absorbed nitrogen increases the meristematic activity of shoots, resulting in greater tillering and leaf area index (LAI). Furthermore, N increases leaf longevity. Such an increase in LAI increases the efficiency of use of solar radiation, measured as the fixation rate of carbon dioxide (μmol of CO2 m−2 s−1), thus increasing accumulation of dry matter.

The accumulation of nitrogen by sugarcane varies according to cultivar, crop age, and availability of N and other elements in the soil solution and also depends on soil and climatic factors. For the more common varieties planted, nitrogen extraction ranges around 1.2 kg per ton of natural matter of shoots. Considering that roots and rhizomes correspond, on average, to 30% of the mass of the whole plant, it can be estimated that for each t of natural matter accumulated by shoots, there is an absorption of 1.5 kg of N by the plant. Therefore, for systems with a productivity greater than 120 tons of natural matter per hectare, the amount of N absorbed by the crop exceeds 180 kg ha−1. In these systems, the use of nitrogen fertilization at doses ranging from 60 to 100 kg ha−1 is suggested [1].

Nitrogen uptake and nitrogen metabolism are greatly influenced by phosphorus availability. In plants with inadequate phosphorus supply, there is a decrease in the nitrate absorption of the soil solution. The nitrate translocation from roots to shoots decreases, thus increasing the accumulation of amino acids in leaves and roots. Ref. [18] observed an enormous influence of the availability of P, both of nutrient and endogenous solution, on corn nitrogen uptake and metabolism (**Figure 4**). Well-supplied phosphorus plants before and during a kinetic study (+P; +P) showed a practically constant nitrate absorption during the experiment. However, plants deprived of P before and during the experimental phase (−P; −P) were unable to absorb the nitrate from the solution.

It is believed that plant cane, because it has a higher phosphorus supply when compared to regrowth, behaves similar to corn plants well supplied with phosphorus (+P; +P). In studies conducted by the authors in the region of Passos, southern Minas Gerais, it was verified that the increase in the dose of phosphorus applied to planting grooves affected larger accumulations of N in the biomass of plant cane, since for each kg of P applied there was an increase of about 1 kg of N. These results are certainly the effects of changes caused in the absorption and metabolism of nitrogen, as observed by [18].

It should be noted, however, that some studies reported a low response of plant cane to nitrogen fertilization, and the causes of such low responses are not sufficiently explained. Several authors have attributed it to experimental variability, to mineralization of organic matter and of crop remains, to fertilizer application times, and to losses by leaching and denitrification [19, 20]. However, in an experiment conducted by [3] with plant cane cultivated in a sandy soil and fertilized with marked urea (15N), losses were not observed with the leaching of nitrogen from the fertilizer (**Figure 5**). The movement of the 15N-fertilizer was small. More than 70% of the fertilizer recovered in the soil was at the 0–30 cm layer. There was a measurable loss of N native from the soil, or of crop remains, equivalent to 4.5 kg ha−1 [3]. Thus, if nitrogen fertilization is applied to plant cane, nitrogen fertilizer, at doses ranging from 60 to 100 kg ha−1, should be applied to the bottom of planting grooves along with phosphorus and potassium.

#### **7.2. Nitrogen in regrowth**

**7. Mineral fertilization**

178 Sugarcane - Technology and Research

**7.1. Nitrogen in plant cane**

the nitrate from the solution.

metabolism of nitrogen, as observed by [18].

CO2

layer and on the productivity desired.

m−2 s−1), thus increasing accumulation of dry matter.

doses ranging from 60 to 100 kg ha−1 is suggested [1].

The mineral fertilization of sugarcane is based on the results of soil analysis at the 0–20 cm

Nitrogen is important for the nutrition and physiology of sugarcane because, among other functions, it is a constituent of all amino acids, proteins, enzymes, and nucleic acids [17]. Nitrogen and potassium are absorbed in greater amounts by this crop [3]. The absorbed nitrogen increases the meristematic activity of shoots, resulting in greater tillering and leaf area index (LAI). Furthermore, N increases leaf longevity. Such an increase in LAI increases the efficiency of use of solar radiation, measured as the fixation rate of carbon dioxide (μmol of

The accumulation of nitrogen by sugarcane varies according to cultivar, crop age, and availability of N and other elements in the soil solution and also depends on soil and climatic factors. For the more common varieties planted, nitrogen extraction ranges around 1.2 kg per ton of natural matter of shoots. Considering that roots and rhizomes correspond, on average, to 30% of the mass of the whole plant, it can be estimated that for each t of natural matter accumulated by shoots, there is an absorption of 1.5 kg of N by the plant. Therefore, for systems with a productivity greater than 120 tons of natural matter per hectare, the amount of N absorbed by the crop exceeds 180 kg ha−1. In these systems, the use of nitrogen fertilization at

Nitrogen uptake and nitrogen metabolism are greatly influenced by phosphorus availability. In plants with inadequate phosphorus supply, there is a decrease in the nitrate absorption of the soil solution. The nitrate translocation from roots to shoots decreases, thus increasing the accumulation of amino acids in leaves and roots. Ref. [18] observed an enormous influence of the availability of P, both of nutrient and endogenous solution, on corn nitrogen uptake and metabolism (**Figure 4**). Well-supplied phosphorus plants before and during a kinetic study (+P; +P) showed a practically constant nitrate absorption during the experiment. However, plants deprived of P before and during the experimental phase (−P; −P) were unable to absorb

It is believed that plant cane, because it has a higher phosphorus supply when compared to regrowth, behaves similar to corn plants well supplied with phosphorus (+P; +P). In studies conducted by the authors in the region of Passos, southern Minas Gerais, it was verified that the increase in the dose of phosphorus applied to planting grooves affected larger accumulations of N in the biomass of plant cane, since for each kg of P applied there was an increase of about 1 kg of N. These results are certainly the effects of changes caused in the absorption and

It should be noted, however, that some studies reported a low response of plant cane to nitrogen fertilization, and the causes of such low responses are not sufficiently explained. Several authors have attributed it to experimental variability, to mineralization of organic matter and of crop remains, to fertilizer application times, and to losses by leaching and denitrification The responses of sugarcane regrowth to nitrogen fertilization are more frequent than in plant cane, with a percentage above 90%. As a general recommendation, it is suggested to apply 1.0 kg of N per ton of natural matter accumulated in shoots. Since industrializable culms represent on average 80% of the natural matter of shoots, yields of 100 t of culms would correspond to 125 t of natural matter. In this case, the recommendation for fertilization would be 125 kg of N ha−1, and the nitrogen fertilizer should be applied in a single dose together with potassium.

Urea has been the most used nitrogen fertilizer for sugarcane fertilization mainly because of its lower cost per unit of N compared to other sources. The application of urea to the soil or straw may lead to large losses due to the volatilization of ammonia (approximately 40%) [1]. Therefore, it is recommended to bury it into the soil at a depth of approximately 7.0 cm. When it is not possible to bury the urea in the soil, it must be irrigated to incorporate it into the soil or to fertilize it before a rain, which is possible only in small areas. If it is not possible to bury

**Figure 5.** Nitrate uptake by corn plants with different phosphorus supplies: adequate before and during the study (+P; +P), adequate before and absent during the study (+P; −P), absent before and adequate during the study (−P; +P), and absent before and during the study (−P; −P). Source: adapted from [18].

urea in the soil, irrigate it, or fertilize it before a rain, one should choose ammoniacal sources, such as ammonium sulfate, or nitric sources.
